We have previously demonstrated the increased metastatic potential of human prostate cancer circulating tumor cells (CTC), compared to their parental cells, in both orthotopic mouse models and the chick embryo model. In the current study, we asked whether an extracellular matrix (ECM), produced by human foreskin fibroblasts in culture, could inhibit PC-3 human prostate cancer CTC metastasis in the chick embryo model. The chorioallantoic membranes (CAM) of 18 chicken embryos were inoculated with either PC-3 human prostate cancer cells or PC-3 CTCs, both stably expressing green fluorescent protein (GFP). Embryos were divided into six groups: PC-3 parental-cell control; PC-3 plus soluble ECM; PC-3 parental cells plus semi-solid ECM; PC-3 CTC control; PC-3 CTC plus soluble ECM, and PC-3 CTC plus semi-solid ECM. Twelve hours following inoculation of the cells, a single dose of 100 μl of either soluble or semi-solid ECM was added to the appropriate group. Embryo brains were removed on day 8 post-inoculation, and were processed for cryosectioning. Imaging was performed on the cryosections using a scanning laser microscope in order to count metastatic foci. PC-3 controls had an average of 11.1 metastatic foci compared to 2.55 in the PC-3 plus soluble ECM group and 2.76 (p<0.0001) in the PC-3 plus semi-solid ECM group (p<0.0001). ECM treatment had even greater efficacy on the CTC cells, with an average of 30.9 metastatic foci in the CTC controls compared to 4.38 in the CTC plus soluble ECM group (p<0.0001) and 4.18 in the CTC plus semi-solid ECM group (p<0.0001). The results demonstrate that reduction of CTC metastatic potential is possible, in this case with an ECM produced by human foreskin fibroblasts in culture.